AD9833 Synchonising

Hi All,

I am a newbie to the forum and fairly novice when it comes to coding & circuit design too.

I'm having an issue with a simple function generator project, in which I am using 2x AD9833 DDS ICs; one for a square-wave trigger/sync signal and one for a sinewave.

I am using a PIC to set the waveform types and then program both ICs to the same frequency. I initialise the phase parameter of the waveforms to some arbitrary, but known, value and the issue I'm having specifically relates to this control of the trigger phase with respect to the sinewave.

What I am seeing is the trigger and/or the sinewave phases seemingly desynchronising. It happens occasionally and randomly when the circuit is powered. The amount they are off seems to be multiples of 45° phase shift. I am guessing that it has something to do with the nature of the waveform being generated, perhaps the starting "draw point" is random?

Is there anyway to ensure that the starting point is repeatably aligned every time?

Many thanks in advance for any suggestions.